Red Oak Tree Leaves Turning Yellow

Red Oak Tree Leaves Turning Yellow

Red oak trees, scientific name Quercus rubra, belong to the genus Quercus, of the beech family Fagaceae. These deciduous trees can grow 80 to 150 feet, and have bristle-tipped leaves and acorns with hairy shell linings. They include the black oak, live oak, willow oak and pin oak. They are fast-growing trees native to North America, and are often grown as ornamentals for their flaming autumn colors. Like most trees, red oaks also suffer from conditions that cause their leaves to turn yellow. This article addresses some of the causes of yellowing leaves and their remedies.

Red Oak Tree Leaves Turning Yellow: What Are The Reasons?

Iron chlorosis

A common reason for yellowing leaves among red oaks is a condition known as iron chlorosis. This is usually observed in USDA zones four to eight and indicates an iron deficiency in the trees. If trees are unable to consume enough iron, their leaves start to turn yellow and may even fall off and die. This condition is associated with a lack of iron in the soil, or the inability to absorb iron due to incorrect soil pH levels. 

To fix the problem, check the soil pH and adjust if needed. Also add iron and other nutrients to the soil if these are depleted. 

Fungal diseases

Red oak leaves turning yellow could also be due to fungal diseases. These infections can spread quickly and one of their manifestations is the yellowing of leaves. 

Here are some common fungal diseases that affect red oak trees:


This disease is caused by the fungus Gnomonia sp., and is characterized by irregular spots forming along the leaf margins or veins. It rarely kills trees, but it defoliates them until they become weakened. 

To fix the problem, rake the infected leaves and destroy or burn them. Fungicide should be applied if the damage persists. Spray in the spring as leaves are emerging, and repeat in one to two weeks’ time. 

Oakleaf blister 

This fungal disease is characterized by a distinct bulge on the upper surface of the leaves. The foliage may turn from light green to yellow, and then brown to black. If the infection is extensive, little defoliation occurs. Apply fungicides on the affected trees to treat this disease. 

Powdery mildew 

This disease causes yellow spots on the surfaces of leaves during the latter part of summer. If there is a severe infection, premature defoliation may occur. The fungus overwinters on infected leaves in its spore stage, which is resistant to adverse weather conditions. Other healthy trees may also be infected as spores are carried by air currents. 

To fix the problem, rake and discard fallen infected leaves and apply fungicides to protect the trees. You need to use a wetting agent with the fungicides to improve coverage on waxy leaves.

Other fungal diseases of red oak trees:

  • Actinopelte leaf spot, caused by the fungus Actinopelte dryina.
  • Endothia canker, caused by the fungus Endothia gyrosa. 
  • Hypoxylon canker, caused by the fungus Hypoxylon atropunctatum.
  • Heart rot.
  • Oak wilt.

Insufficient water

Like all plants, red oak trees need water, and if they do not consume enough, their leaves could turn yellow. You can alleviate this problem by installing irrigation systems for proper hydration. This will enable the trees to stay healthy and hydrated despite long drought spells. 

Sudden oak death 

The sudden oak death, or Phytophthora ramorum, is a type of root rot disease that commonly affects oaks. This algae-like organism could also cause the leaves to turn yellow and fall off. 

To reduce the risk of this disease, plant your red oak trees in areas with proper water drainage and give them just enough water for their needs. 

Red Oak Tree Care

Red oak trees require minimal care, but young or new trees need regular moisture, especially during hot weather. Water the young trees deeply at least once weekly, especially when there is no rain. Established red oak trees are more drought tolerant. If you notice the presence of powdery mildew during humid weather, treat it immediately with a fungicide. If there are pests like aphids, spray the foliage with a strong jet of water, or use insecticidal soap sprays.


Red oak trees are North American ornamental and timber trees popular for their fiery foliage during the autumn season. They can also be prone to yellowing leaves, which could be due to iron chlorosis, fungal diseases, insufficient water, or sudden oak death.

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